The present invention relates to a signal transmission method in a base transmission station device of cellular radio communication and in particular, to a beam forming method for transmitting a signal in a particular direction by using a plurality of antenna elements such as an array antenna.
In the cellular radio communication, an array antenna is used to improve an antenna gain and reduce interference to other communication. The array antenna uses a signal processing technique called “beam forming”, i.e., a signal transmission or a signal reception is performed by applying an array weight made of a complex number to a plurality of antenna elements so as to give a directivity pattern for emphasizing the antenna gain in a particular direction. The array weight is generally controlled by digital signal processing and can be freely modified at a particular timing. Thus, it is possible to adaptively modify the antenna gain in response to the user motion and always perform adaptive processing giving an optimal antenna pattern. Moreover, in the OFDM communication, when transmitting a signal by decomposing the signal into frequency components orthogonally intersecting each other by a signal processing using the FFT, the aforementioned array weight is multiplied for each tone of the decomposed frequency so as to give a different antenna pattern for each of the frequencies. For example, IEEE C802.20-05-59rl http://ieee802.org/20/DFDD Technology Overview Presentation (Nov. 15, 2005) (Non-patent document 1) discloses a processing for modifying the array weight for each of the users in the OFDMA (Orthogonal Frequency Domain Multiple Access).